For protection against transmittable infectious diseases it is customary to vaccinate humans and animals with immunogenic material against which protective anti-bodies can be formed.
For this purpose, for example, the pathogen itself can be administered in a live, but preferably non-infectious form, or the killed pathogen or an antigen fraction of the pathogen in which the infectious component is lacking can be administered.
In these latter two cases it is necessary also to add to the antigen one or more components which stimulate the immune response of the organism to be protected. Such immune response-stimulating components are usually referred to by the term adjuvants. Freund's complete adjuvant is a water-in-oil (w/o) emulsion of mineral oil and killed mycobacteria and is regarded as one of the most powerful adjuvants. Other known adjuvants are emulsions of mineral oils, such as Freund's incomplete adjuvant, and of vegetable oils, such as peanut oil, maize oil, cottonseed oil and sunflower oil, and semi-synthetic oils, such as MIGLYOL.TM. 812N and MYRITOL.TM. oil.
However, the abovementioned emulsions, especially water-in-oil emulsions based on mineral oil, cause serious tissue irritations, inflammation swellings and cysts at the site of administration, for which reason the routine use of these emulsions in humans and animals is less desirable and in certain cases is even prohibited. Moreover, vaccines based on w/o emulsions are relatively viscous, which makes injection of the vaccine more difficult.
Reducing the oil content causes such a rise in the viscosity that the vaccine can no longer be injected. At the same time this can have an effect on the stability of the emulsion.
The use of .alpha.-tocopheryl acetate as a water-in-oil emulsion in a vaccine for the protection of rams against infection with Brucella ovis was described by Afzal et al., Veterinary Immunology and Immunopathology 7 (1984), 293-304. However, the vaccine contains approximately 50% dl-.alpha.-tocopheryl acetate, as a result of which the vaccine becomes viscous and consequently is difficult to handle.